1. Field of the Invention
The present invention pertains to disposal of slurried solids wastes and the like in a hydraulically fractured earth formation in a relatively permeable disposal zone disposed below a relatively impermeable overburden zone and above an underburden zone having higher in situ compressive stresses than the disposal zone.
2. Background
One suitable way of disposing of solid waste materials comprises reducing the particle size of the solids material, slurrying the finely ground solids with a suitable disposal or carrier liquid and injecting the slurry into a relatively deep earth formation zone which will prevent uncontrolled movement of the waste material into zones from which fluids such as fresh water may be produced. U.S. Pat. No. 4,942,929, issued Jul. 24, 1990, to Malachosky, et al and U.S. Pat. No. 5,109,933, issued May 5, 1992, to James E. Jackson, both assigned to the assignee of the present invention and U.S. Pat. No. 5,108,226, issued Apr. 28, 1992 to Jennings, Jr. describe methods for disposing of slurries of solids particles and a suitable carrier liquid such as fresh or salt water by injection of the slurries into deep wells and fracturing an earth formation to provide for disposal of a suitable quantity of the waste material.
Moreover, U.S. patent application Ser. No. 07/910,381, filed Jul. 8, 1992, in the name of Thomas K. Perkins and U.S. patent application Ser. No. 08/008,375, filed Jan. 25, 1993 to Winton G. Aubert, et al, both assigned to the assignee of the present invention, describe certain improvements in techniques for disposal of liquid and slurried solids waste in deep earth formation disposal zones. The method described in application Ser. No. 07/910,381 is unique in that formation zones having alternate layers of permeable and relatively impermeable material may be advantageously utilized to dispose of relatively large quantities of slurried solids wastes. However, deep earth disposal zones which have the characteristics which may be taken advantage of in the method described and claimed in application Ser. No. 07/910,381 may not be readily available in locations which may otherwise be desired for disposing of wastes which generally comprise slurries of relatively small particles of solids material.
It is more common to find earth formations having one or more relatively permeable zones of substantial thickness or vertical span which are located below a formation zone comprising overburden of relatively impermeable material and which may exhibit an in situ compressive stress field generally greater than the more permeable zone. Such formations also, generally, exhibit gradual or significantly increasing in situ compressive stress with depth even though certain zones at different depths may have relatively lower in situ compressive stresses than either the overburden or the underburden of the particular zone in question. Such earth formation zones may be advantageously used for the disposal of slurried solids wastes in accordance with the present invention.